This invention relates to a photocurrent sensor circuit, and more particularly, to a two-wire photocurrent sensor circuit.
Gas turbine flame intensity may be measured and utilized in the gas turbine engine for efficient operation. The flame in a gas turbine engine generates electromagnetic emissions in the visible, infrared, and the ultra-violet electromagnetic spectrum. Ultra-violet emissions of particular interest occur in the range from about 200 to about 400 nano-meters. The silicon-carbide photocurrent sensor has demonstrated it's ability to respond well to ultra-violet emissions in a background of infrared emissions and visible emissions, while being relatively insensitive to the infrared and visible emissions, as is disclosed in U.S. Pat. No. 5,394,005. A five-wire photocurrent detector circuit is disclosed in U.S. Pat. No. 5,589,682, hereinafter identified as Patent '682, which describes a silicon-carbide photocurrent detector. Patent '682 discloses a photocurrent detector circuit coupled to five wires, each wire having one of the following functions: positive power supply coupling; negative power supply coupling; ground coupling; and couplings for each of two output signals. It is advantageous to minimize the number of wires in gas turbine so as to reduce the complexity, cost, and maintenance. It is thus desirable to employ a silicon-carbide photocurrent detector circuit capable of operating effectively with as few connections as possible.
A gas turbine engine typically operates over a wide temperature range. The flame generated by the gas turbine engine typically generates temperatures above 2000 degrees Celsius (C). Hot sections aft of the combustor of a gas turbine may be heated to 300.degree. C. It is desirable to employ a photocurrent detection circuit that will measure photocurrent accurately at temperatures up to 300.degree. C.
Reducing the number of components in a photocurrent detection circuit provides potential cost and reliability benefits, making it desirable to employ a photocurrent detector circuit employing as few components as necessary.